Trigger Oracle PLSQL

SQL> -- create demo table
SQL> create table Employee(
  2    ID                 VARCHAR2(4 BYTE)         NOT NULL,
  3    First_Name         VARCHAR2(10 BYTE),
  4    Last_Name          VARCHAR2(10 BYTE),
  5    Start_Date         DATE,
  6    End_Date           DATE,
  7    Salary             Number(8,2),
  8    City               VARCHAR2(10 BYTE),
  9    Description        VARCHAR2(15 BYTE)
 10  )
 11  /
SQL>
SQL> -- prepare data
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2               values ('01','Jason',    'Martin',  to_date('19960725','YYYYMMDD'), to_date('20060725','YYYYMMDD'), 1234.56, 'Toronto',  'Programmer')
  3  /
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('02','Alison',   'Mathews', to_date('19760321','YYYYMMDD'), to_date('19860221','YYYYMMDD'), 6661.78, 'Vancouver','Tester')
  3  /
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('03','James',    'Smith',   to_date('19781212','YYYYMMDD'), to_date('19900315','YYYYMMDD'), 6544.78, 'Vancouver','Tester')
  3  /
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('04','Celia',    'Rice',    to_date('19821024','YYYYMMDD'), to_date('19990421','YYYYMMDD'), 2344.78, 'Vancouver','Manager')
  3  /
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('05','Robert',   'Black',   to_date('19840115','YYYYMMDD'), to_date('19980808','YYYYMMDD'), 2334.78, 'Vancouver','Tester')
  3  /
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values('06','Linda',    'Green',   to_date('19870730','YYYYMMDD'), to_date('19960104','YYYYMMDD'), 4322.78,'New York',  'Tester')
  3  /
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values('07','David',    'Larry',   to_date('19901231','YYYYMMDD'), to_date('19980212','YYYYMMDD'), 7897.78,'New York',  'Manager')
  3  /
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values('08','James',    'Cat',     to_date('19960917','YYYYMMDD'), to_date('20020415','YYYYMMDD'), 1232.78,'Vancouver', 'Tester')
  3  /
SQL>
SQL>
SQL>
SQL> -- display data in the table
SQL> select * from Employee
  2  /
ID   FIRST_NAME LAST_NAME  START_DAT END_DATE      SALARY CITY       DESCRIPTION
---- ---------- ---------- --------- --------- ---------- ---------- ---------------
01   Jason      Martin     25-JUL-96 25-JUL-06    1234.56 Toronto    Programmer
02   Alison     Mathews    21-MAR-76 21-FEB-86    6661.78 Vancouver  Tester
03   James      Smith      12-DEC-78 15-MAR-90    6544.78 Vancouver  Tester
04   Celia      Rice       24-OCT-82 21-APR-99    2344.78 Vancouver  Manager
05   Robert     Black      15-JAN-84 08-AUG-98    2334.78 Vancouver  Tester
06   Linda      Green      30-JUL-87 04-JAN-96    4322.78 New York   Tester
07   David      Larry      31-DEC-90 12-FEB-98    7897.78 New York   Manager
08   James      Cat        17-SEP-96 15-APR-02    1232.78 Vancouver  Tester
SQL>
SQL>
SQL>
SQL> create table employees_copy as select * from employee;
SQL>
SQL> create table employees_log(who varchar2(10),
  2                             action varchar2(10),
  3                             when date );
SQL>
SQL>
SQL>
SQL>
SQL> desc employees_log
 Name                                                                                                  Null?    Type
 ----------------------------------------------------------------------------------------------------- -------- --------------------------------------------------------------------
 WHO                                                                                                    VARCHAR2(10)
 ACTION                                                                                                 VARCHAR2(10)
 WHEN                                                                                                   DATE
SQL>
SQL> create or replace trigger biud_employees_copy
  2    before insert or update or delete
  3       on employees_copy
  4  declare
  5    l_action employees_log.action%type;
  6  begin
  7    if INSERTING then
  8      l_action := 'Insert';
  9    elsif UPDATING then
 10      l_action := 'Update';
 11    elsif DELETING then
 12      l_action := 'Delete';
 13    else
 14      raise_application_error( -20001,
 15          'You should never ever get this error.' );
 16    end if;
 17
 18    insert into employees_log(
 19      who, action, when )
 20    values(
 21      user, l_action, sysdate );
 22  end;
 23  /
SQL>
SQL> insert into employees_copy(id,last_name,Start_date)  values
  2                            ( 1234,'Beck', sysdate);
SQL>
SQL> select * from employees_log;
WHO        ACTION     WHEN
---------- ---------- ---------
RNTSOFT     Insert     09-SEP-06
SQL>
SQL> update employees_copy
  2    set salary = 500000.00;
SQL>
SQL> select * from employees_log;
WHO        ACTION     WHEN
---------- ---------- ---------
RNTSOFT     Insert     09-SEP-06
RNTSOFT     Update     09-SEP-06
SQL>
SQL> drop table employees_log;
SQL>
SQL> drop table employees_copy;
SQL>
SQL>
SQL> -- clean the table
SQL> drop table Employee
  2  /
SQL>
SQL>